Differential pressure gauge



May 30, 1950 w. J. KINDERMAN 2,509,644

DIFFERENTIAL PRESSURE GAUGE Filed Jan. 6, 1944 v 8 sheets-sheet 1 99 @i -yw Ul 962 17 i *iiiimiem May 30 1950 v w. KINDl-:RMAN 2,509,644

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DIFFERENTIAL PRESSURE GAUGE Filed Jan. 6, 1944 8 Sheets-Sheet 15 s. @MNM Mw May 30, 1950 'w. J. KINDERMAN 2,509,644

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May 30, 1950 Filed Jan. 6. 1944 W. J. KINDERMAN DIFFERENTIAL PRESSURE GAUGE 8 Sheets-Sheet 7 ToRquiDzvELoPeo Wrr H Ras PCT EJ VlAciN Tlc Novem E NT WIDTH OF MAGNETI c POLES eveRALTl r1 :s SPIRALTmcKNss:

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W. J. KINDERMAN DIFFERENTIAL PRESSURE GAUGE Tus. NmnencGAr hnumc MonsmAnns Wma RssvgnrTo May 30, 1950 Filed Jan. 6, 1944 Snowmq Srmn. Anrwfuncecnwsl Ann RLSToRlNqToRqueWITH Raspec ToNAqNm-m F1 own am* Tanque. Dcvupeo In BALANCE@ SPIR M Patented May 30, 1950 DIFFERENTIAL PRESSURE GAUGE l Waiter J. Kinderman, lhiladelphia, Pa., assignor to Yamini-Waringr Company, Chestnut Hill, Philadelphia, Pa., a corporation ot Pennsyl- Application January 6, 1944, Serial No. 517,242

30 Claims.

My invention relates to means for transmitting longitudinal motion within a chamber subject to pressure into rotary movement outside the chamber through a pressure resistant wall, nding its greatest utility at the present time in water-level indicators for boilers.

A purpose is to operate anindicator or recorder by a spiral magnetic armature through movement of a magnet along the length of the armature.

A further purpose is to provide spiral connection between a pressure-responsive element such as a diaphragm, bellows or oat, and an indicator through a magnet and magnetic armature, geared together magnetically to produce a result similar to worm and worm gear connection.

A further purpose is to use difference in pressure, such as characterizes difference in water levels or is present on opposite sides of an oritice in a ilow meter, for example, to shift the position of a magnet along the length of a rotary spiraled magnetic armature and to show angular movement of the armature upon an lndicator.

A further purpose is within a pressure chamber to provide a magnet movable by reason of differences in pressure due to water level fluctuation in a boiler, with a spiraled magnetic armature connected with an indicator and protected from boiler pressure as by a well.

A further purpose of the invention is to apply magnetic linkage between a magnet preferably of horse-shoe type movable transversely to its flux and a rotatable spiral armature of magnetic material between the poles having its axis longitudinal to the direction of motion to secure rot/ary motion of the armature and connected parts. This is particularly useful because the magnet coupling is resilient and because it operates through pressure-resistant walls so that the magnet can be subject to pressure and the armature free from pressure.

A further purpose is to provide effective and accurate connection between a pressure-sensitive element subject to differing pressures, one varying because of diiierent water levels or both due to ow meter pressure drop, for example, and to indicate magnet movement through rotary armature actuation.

A further purpose is to provide eiective and accurate connection between a pressure-sensitive element, subject to variable heads or to the two pressures on opposite sides of an orifice, and an indicator, while avoiding stuiling box friction and other friction.

A further purpose is to provide for spring support of an indicator-controlled magnet with adjustment of the fulcrum about which the spring operates as well as an arbitrary zero position of the magnet.

A further purpose is to support a magnet by a iiat spring, varying the fulcrum of the spring by means adjustable along the length o! the spring.

A further purpose is to support a magnet by a flat spring and to set any arbitrary Zero position of the parts by bending the spring.

A further'purpose is to support a horseshoe magnet upon a pool such as mercury and subject different parts of the surface of the pool to a standard pressure and to a variant pressure respectively, represented by different liquid levels, or to pressures on opposite sides of an orice during flow, and to convert movement oi' the magnet into indicating turning movement of a spiraled magnetizable armature located between the poles of the magnet.

A further purpose is by iloat means to shift a horseshoe magnet in a direction generally longitudinal of a rotatable magnetizable (herein frequently referred to as magnetic) armature located between the poles of the magnet, using turning of the armature to operate gauge parts.

Further purposes will appear in the specincation and in the claims.

I have preferred to illustrate my invention by a few forms only, selecting forms which are simple, practical, reliable, eective and inexpensive and which at the same time weii illustrate the principles involved.

Figure l is a central vertical section of a preferred form of my invention.

Figure la is a fragmentary section applying to the structure of Figure l, a modified form oi' pressure-responsive element.

Figure 1b is a reduced scale fragmentary illustration of a form modified as compared with Figure 1.

Figure 2 is a reduced scale section of Figure l, taken on line 2-2 of Figure l.

Figure 3 is a reduced scale perspective view of a portion of the structure oi Figure 1, capable of use also with the structure of Figure 1a.

Figure 4 is a reduced scale central iongitudinai section of a second form of my invention, taken upon line 4--4 of Figure 5.

Figure 5 is a section of Figure 4, taken upon line 5-5 of Figure 4.

Figure 6 is a fragmentary longitudinal central section of a third form of my invention.

' asomo Figure 6.

Figure 8 is a diagrammatic elevation partly in section showing the invention applied as a liquid level gauge in a high pressure boiler with the gauge located in position to be read from the floor. Y v

Figure 9 is 4a. diagrammatic elevation, partially in section showing the invention applied to flowmeter measurement of a liquid passing through an orifice.

Figure 10 is a fragmentary elevation partly in section showing the invention applied to-recording flow through a weir notch.

Figure 10a is a fragmentary front elevation of a V-notch weir such as could be used in Figure 10.

Figure 10b is a side elevation or top plan view of one oi' many possible forms of follower or armature to correct in the armature where the variation in rate or quantity of flow is not the same at all parts of the amature for equal movements oi' an operating magnet.

Figure 11 is a fragmentary section of another Weir meter having much simplified connection with an indicator.

Figure 12 is a front elevation of a pen recording device operating on a travelling sheet by which any oi' the flow indicating structures can be made recorders.

Figures 13, 13a; 14, 14a; 15, 15a and 16, 16a are schematic figures arranged in pairs and illustrating conditions concerning the poles and the spiral armatures as they apply to previously existing structures.

Figures 17, 17a and 18, 18a are corresponding pairs of schematic views relating to the present invention.

Figures 19, 20, 21, 22 are schematic views showing relations existing between the poles and the armature in the present invention.

The present application is a continuation in part of applicants previous application, Serial No. 388,134, illed April 11, 1941, now abandoned.

'Ihe subject matter relating to liquid level variation or the like, particularly as illustrated in Figures 9, 10, 10a and l1, is included in my copending application Serial No. 713,035, filed November 29, 1946,` for Meter.

The pressure sensitive element in some of the forms uses a pressure area or surface which is exposed to fixed and variant opposed (hence differential) pressures. It acts against a restraining force which increases uniformly with progressive displacement of the pressure area.

The preferred form among those shown is a diaphragm subject to the opposing pressures, using a flat cantilever spring as the restraining force.

It is evident that various other forms will carry out my broad invention and I have illustrated several.

A metal bellows (Figure 1a) of spring material of proper proportions could be used instead of the diaphragm. y

A magnet float within a mercury pool is cheap and effective, part of the pool being subject to one of the diierential pressures and part exposed to the other pressure.

Because it is my understanding that I am obligated to explain fully one vway in which my invention may be practiced, and that way the best way known to me, I describe many parts of my device in what may seem to be excessive detail, whereas obviously other structure can be used to take their place.

The operating mechanism for my preferred form of indicator, that of Figures 1, 2 and 3 is enclosed within a housing l5 and cover I6 united by bolts I1 and sealed by annular packing il, I9 lying on opposite sides of a diaphragm support 23 apertured at 2|.

The diaphragm support for convenience is recessed at 22 on the side toward the housing body 23 in order to permit a well, later described, to fit down into the recess.

Because the liquid whose level is to be indicated does not enter the housing but produces its eil'ect in alteration of effective pressure to be exerted upon the diaphragm through fluid piped to the housing from a distance, there is no requirement that the housing be placed in any particular position with respect to the vertical or horizontal. It is therefore .assumed to be mounted vertically from any suitable bracket by a bolt entering threaded opening 24. This corresponds with the showing in Figure 1. The indicator used may therefore be attached to the front face of the housing where it can be seen to the best advantage. With this arbitrary position for the gauge the parts will be considered conveniently as outer and inner, upper or lower, according to their relation in Figure 1.

On the inner side of the diaphragm support, toward the cover, the support is annularly recessed at 25 to permit collapse into the recess of an annular transversely free flexible diaphragm portion 26 of a diaphragm 21. The diaphragm is held at its outer edge by the packing I9 which protects against leakage between the diaphragm support and the cover.

At its center the diaphragm is stiifened and supported to move as a unit, by diaphragm plates or heads 29 and 30 which are fastened together. The cover is concaved at 3i to give room for the diaphragm and its plates within the cover.

The plates are held to the diaphragm on opposite sides between members 32 and 33, threaded together. One of the members is cupped at 34 for convenient application to it of a desirable form of thrust connection between the diaphragm and parts which are to be moved by it. As in the case of most of the structures, various forms of carrying out my functions are available.

In the thrust transmission shown the clamp member 32 is apertured at 35 for passage of a pin 36 and the clamp member 33 is coned concavely at 31 to form a pin bearing support for the end 38 of the pin 36.

The diaphragm is subjected to differential pressure on opposite sides through pipes 39 and 40 which may represent differences in fluid level, or in pressure on opposite sides of an orifice, or flow over a weir, for examples.

The pressure upon the inner face, adjacent the cover, is a standard pressure in the liquid form, shown equal to or greater than the pressure attained due to the highest level of liquid to be indicated.

y The pin 36 carries a collar at 4I in order to prevent accidental withdrawal from the clamping members through aperture 35.

At the other end the pin 36 is pointed at 42 to engage within and form a pin bearing with a concavity 43 in a thimble 44 which engages with the spring 45. The end 46 of the thimble passes through an aperture of the spring and may be peened at 41 to place against the spring to hold the parts together. Peening is not necessary because the parts are under compression.

Whatever the form of connection between the pressure sensitive device (diaphragm) and the magnet, the spring makes a very convenient support for the horseshoe magnet Il and supplies magnet. 4

Where the thimble and pin 'connection are used, the support of the thimble from the spring and the mounting of the horseshoe magnet may be stiilened and reinforced by holding the horseshoe magnet to the spring by the same bolts 49 which fasten a plate 50 upon the under side of the magnet, thus uniting the thimble and plate 50. When this is intended the thimble is hanged at 5l to engage the plate about an opening 52 through which the rear end 5I of the thimble passes. Ihis rear end of the thimble is constructed initially in the shape seen in dotted lines. After it has been passed through the opening it is peened over against the plate in the position shown.

By whatever means the magnet Il is shifted transversely with respect to its planes and to its lines of flux, whether by a pressure-operated diaphragm or bellows, for example, or as by a float, the means for transmission of the response of the pressure-sensitive element consists basically of passing magnetic flux from apermanent magnet, subject to pressure through a pressure wall or well 54 to a magnetically susceptible rotatable follower, or armature 55 which is external in the sense that it is free from pressure but at the same time is responsive rotarily to movement of the magnet parallel to the axis of the follower and within the pressure chamber.

More specifically, the magnetic transmission is based on change in reluctance of the magnetic circuit with movement of the magnet at right angles to its flux and along the axis of the armature, accompanied by rotary reaction of the armature to the magnet movement to essentially re-establish the reluctance of the magnetic circuit at a balanced position which is thus maintained as a constant.

It is important that the magnetic reluctance for the balanced position oi' the armature through the range of movement of the pressure sensitive element remains essentially constant in order to avoid the effect of unbalanced magnetic forces upon the indication.

The magnet is a permanent magnet of material capable of holding its magnetism over prolonged periods of time without change, Its poles 56 and 51 are shown as curved to partly inclose the walls of the well but, where the magnet is canted during its movement along the axis of the armature, the magnet poles must have clearance from the armature suflicient so that the poles will not touch the walls of the well when the magnet has been shifted along the armature axis.

Pole faces have been used successfully which are not curved.

Necessarily with lateral movement of the magnet in the form of Figures 1 to 3 the spring mount in tilting about a fulcrum will cant the magnet so that its outer and inner surfaces 58 and 59 will no longer be parallel to their positions as seen in Figure 1 and the center line between the poles parallel to their curved surfaces will no longer be parallel with the axis of the armature 55 and of well 54.

In order to give suillcient clearance various means may be used. The total clearance may be made large, or the edges of the poles at 60 and il may be relieved to permit this canting with close clearance, or the faces l2 and 83 of the poles may be relatively attened so as not to present true cylindrical surfaces. In Figure 6 the poles terminate in parallel spaced plane surfaces 64. Whatever the means used for insuring clearance, when the magnet tilts as it moves, the poles should be free from contact with the well throughout the intended range of magnet movement.

While, as suggested, magnets with parallel plane pole surfaces of uniform cross-section may be used with the well located directly between them and with high flux density (see Figure 6) better results in most cases are obtained with magnet poles shaped t0 conform as nearly to the well as the law of movement of the magnet will permit and without contactfwith the well. It is also desirable to keep the clearance as uniform as possible throughout the range of motion oi' the magnet.

Any good magnetic alloy which is capable of holding its magnetism well can be used for the magnet. Good results have been secured by the use of a cast magnetic material known as alnico. Of course any electromagnet may be used to serve instead of the permanent magnet but practical diillculties of connection, and particularly that it is dependent upon an outside current source, makes this undesirable. Such a magnet is used in Figure 11 fed through wires 48a, 8b. With higher iiux densities, smaller magnets may be used.

The magnet movement is desirably as nearly as possible parallel to the axis of the armature and to the axis of the well in order that the clearance of the magnet poles from the well may be made and maintained as small as possible. ln such a form as that of Figure l, with a support which bends about the fulcrum of a spring, the magnet will travel through a curved path determined by the position of the fulcrum and the approach which the bend of the spring about its fulcrum affords to true swinging movement about an axis in the fulcrum.

The armature comprises a spirally twisted strip made of flat magnetically susceptible material as close fitting to the well as possible without contact of the edges of the spiral with the interior walls of the well, in order that this material may as nearly as possible completely span between the two magnet poles. The magnetically susceptible material is referred to herein variously as "magnetizable and magnetic The well is threaded at 65 into the housing. It is also threaded internally at 36 and is closed at the outer end by a plug 6i. Within the plug 6l and within an insert plug BB at the bottom of the well are located jeweled bearings 6@ and l0. The plug and the bearing t@ permit passage through the plug and outer bearing of a shaft 'H rigid with the armature and carrying a pointer or needle 12, counter-balanced by Weight T3.

t is necessary, of course, to adjust the indication or recording position to the actual liquid conditions of water level or dow. Because of the structure of the gauge, zero here is a high water level point rather than a low water level point.

Because the gauge depends for its operation upon a higher standard pressure or higher variable pressure with a lower variable pressure, and in water level indication depends upon a standard high pressure with a variable lower pressure, the standard high pressure is used as the zero point to which the setting of the zero posiasoaou tion of the spring in Figures 1, 2 and 3 is related. For this reason the standard pressure is introduced to the right of the diaphragm in Figure 1 and the variable lower pressure is introduced to the left of the diaphragm in Figure 1.

With a. longer pitch the range of movement of a needle 12 is reduced for any given movement of the magnet along the axis of the armature, whereas with a shorter spiral pitch the corresponding range of angular movement and of movement of the needle 12 about its scale is increased. Of course the calibration of the scale must be suited to the movement provided.

The scale may be calibrated to suit any unusual or irregular needle or. pen movement by which it differs from angular movement truly proportional to the change in liquid level or change in rate of flow. In Figure 10b I indicate a correction of the armature movement by variation of the spiral pitch from a true spiral of uniform pitch.

Assuming that the rate of iiow through a meter or Weir, orice or Pitot tube type, for example, is being indicated or recorded, the need for calibration differently than a uniform calibrated scale may be eliminated or greatly reduced by progressively shortening the pitch of the spiral for the Weir type or progressively lengthening the pitch in the orifice or Pitot tube type with respect to liquid level or pressure variation in the particular meter selected. Where the ow varies with the 5/2 or 3/2 power with respect to the liquid level, according to the weir notch used, the pitch of the spiral will be reduced progressively to correspond so as to cause an increasing movement of the needle or recording pen for each successive equal increment of rise in liquid level.

Many examples might be cited where, unless corrected, the needle movement per unit of pressure diiierence would vary from uniform movement.

Variation of spiral pitch from uniform pitch to correct the movement of an indicating needle or recording pen responsive to differences in pressure in a iiow meter on opposite sides of an orifice takes care of variation between the two pressures which may both be variable.

In Figure b the magnet follower or armature 55 progressively reduces in pitch from the inner end 14 to the outer end 14 and the recorder pen 15 is correspondingly accelerated in angular movement when the magnet moves along the follower in this direction with increasing liquid levels or pressure differences.

With orice flow the armature would be altered in pitch reversely to what is shown in Figure 10b, the pitch progressively lengthening from the right to the left as distinguished from the showing in 10b, to take care of the square root function applying to orifice iiow.

The zero point of the indicator needle or recording pen can be adjusted by turning the needle or recorder to zero at zero position of the magnet and setting the needle or pen at its zero by a set screw 16 bearing against shaft 1|.

The jewel mounting of the spiral armature permits practically frictionless rotation of the armature about its axis, which is the axis of the well and` in practice no diiculty has been found in securing sufcient angular extent of rotation for direct reading, avoiding the friction and lost motion which would be introduced by insertion of gearing to multiply in needle or pen movement the angular movement of the armature.

The armature is preferably of soft iron or low carbon steel. Excellent results have been secured with Swedish iron and with so-called core iron having high permeability, low reluctance and low hysteresis. An annealed low carbon iron or steel oi' commercial grade can be used. The armature will operate even when it in itself constitutes a spiral magnet but will not operate as satisfactorily as when it is made of soft iron.

The well is of nonmagnetic material.

bronze has given good results.

- The section of the spiral within the well which is directly between the poles of the magnet becomes part oi' the magnet circuit, the reluctance of which depends upon the angular relation with respect to the poles of that part of the spiral within this range of magnetic iniiuence, i. e. the phase relation of the spiral to the iiux at which the delicately mounted armature comes to rest. Since the spiral is free to turn, lowest and essentially constant reluctance considerations cause the spiral to assume a position of lowest reluctance to the magnetic eld. Whatever position the magnet poles assume along the axis of the armature, the lowest energy relation of the spiral section between the poles will be the same lowest energy relation and the same phase relation, i. e. the same as that in the initial position of vthe magnet. Assuming that this always corresponds to alignment of the spiral section at the magnet pole centers withthe flux, this will result in such rotation of the armature for any magnet movement that the armature length between the poles will correspond angularly to that seen between the poles in Figure 1.

Where the armature pitch is uniform, as in Figure 1, the relation of the spiral to the magnet will be constant, i. e., the armature will rotate equally for each increment of magnet movement causing angular rotation of the armature and hence of the indicator or pen to equal extents for equal ranges of movement of the magnet along the armature axis.

The method of transmission of movement oi' the diaphragm or other pressure sensitive element into rotative eiect upon the indicator results in the transformation of a comparatively small transverse motion of the pressure-sensitive element into a large angular motion of the spiral and attached pointer or recorder, with an accuracy and reliability quite comparable with that which could be secured if the armature and magnet were coupled mechanically as a worm and Worm gear, but free from gear friction and free from stuffing box requirements between the pressure chamber and the indicator.

Basic design considerations indicate that the relation of spiral pitch to magnet thickness should be relatively high. A 4 to 1 relation gives good results and 3 to 1 gives quite acceptable performance. .The ratio of spiral strip thickness to width is not so critical but does affect sensitivity, torque and hysteresis effects. Thin strip spirals show superior sensitivity and lower hysteresis lag while thicker strips show less sensitivity and higher hysteresis lag but with a slight gain in maximum obtainable torque values.

Other forms of adjustment for zero position and for range of indication previously referred to are based upon the mounting and shape of the spring 45, i. e. upon controlling the initial restraint and the variation in restraining force with displacement of the pressure area of the Silicon pressure-sensitive element, as applied to the 9 particular type oi' restraint selected in Figure 1. In the present construction this is accomplished by positioning an adjustable fulcrum support (edge) against e. at restraining spring such as that of Figure 1.

Movement of the fulcrum edge normal to the plane of the spring controls the zero setting, while movement of the fulcrum edge along the surface of the spring parallel to the spring length changes the unsupported spring length and therefore the deflection characteristics. This is equivalent to calibration for range of liquid level travel or range for a given indication.

Space limitations require a special design of the flat spring to obtain the adjustment range desired within permissible spring stresses. The spring material must be corrosion-proof and free from creep, fatigue and appreciable elastic hysteresis. Good results are obtained with heat treated beryllium copper.

The spring 45 is supported at its rear end between a transverse block 1l and its cap 18, both held to the body of the housing by bolts i9.

If the supporting spring were the same thickness and width throughout its length the possible adjustment in range of movement due to fulcrum adjustment would be relatively small, whereas it is desirable to have the construction cover a range of level difference up to two or more feet. To increase the eifect of change in fulcrum the spring can be varied in thickness, or, as is here more convenient and desirable, in the effective width where the spring is bent, i. e., at the fulcrum.

In order to accommodate a wide. difference in range, the supporting atspring is wide and is slotted at 80 at its supported end 8|, the end opposite that which carries the magnet, and the walls adjacent the bifurcation are tapered at 82 and 83. The outer walls taper inwardly and upwardly toward the upper end at 84 and 85.

Though the spring is at all times supported by the block 1l and its cap, the effective length of the spring is determined by an adjustable fulcrum in the form of a bar 88 having knife edge 8l extending across the spring. The bar 86 is movable transversely to the length of the knife edge, i. e., longitudinally of the spring.

It will be evident that with the taper at the outer end of the bifurcation and the outer edge taper at the upper end of the spring, movement of the knife edge lengthwise of the spring in Figure l will increase the width of the spring which is engaged by the knife edge and consequently will increase the Width of spring which must be flexed in order to bend the spring.

The movement of the knife edge toward the connection with the diaphragm also shortens the leverage available for bending the spring by pressure through the diaphragm, hence, with lowering movement of the fulcrum in Figure 1, three elements, the progressive (inward) widening of that part 'of the spring section` engaged near the middle of the width of the spring, the progressive (outward) widening of that part of the spring section engaged near the outer edge of the spring and the shortening of the leverage, will progressively reduce the distance to which the spring will be bent by any given pressure exerted through the diaphragm.

The complete range of movement of the magnet and hence of needle indicator or recorder movement for a given water level variation or pressure difference will be reduced progressively by inward movement of the fulcrum knife edge in 10 Figure 1. or will be increased progressively by movement of the knife edge fulcrum outward in that figure. lThe fulcrum is shown in Figure 1 at. its outermost position, corresponding with the longest range of movement of the magnet and greatest armature turning movement for a given pressure difference across the diaphragm.

The block carrying the knife edge fulcrum is slotted transversely at 88 from the back 89 so as to permit the block to be slid from the right in Figure 1, upon the barrel 98 of a spool 9| having flanges 92 and 93, when the spring is not in place.

The spool is rigid with a screw 94 which is threaded at 95 into the block or at 96 into the flange of the housing, or preferably into both of them, so that a slot 91 in the end of the screw may be accessible for turning to advance or retract the screw, and hence the spool, along the length of the spring. Access to the screw 94 is had through bore 98 within the fiange, exceptl as this bore is closed and leakage from within the housing is prevented by a set screw 99 which holds in place packing i90.

The flanges 92 and 93 hold the bar in position so as to place it at any desired position along the length of the spring and to hold it there.

During the travel of the slotted bar along the length of the spring, the back of the bar, i. e. the left end face of it in Figure l, engages a disc IUI carried by a screw |02 which is threaded into the housing at H13 and can be advanced or retracted to move the disc i0! from or into a recess |04. The control of the screw I02 and the protection against leakage here are similar to those shown for the fulcrum screw.

Since the setting of the zero point of the indicator is dependent upon the position of the magnet to right or left in Figure 1, the zero point can be adjusted by advancing or retracting the disc IBI in that figure and correspondingly pushing the fulcrum edge against the spring or releasing it with respect thereto. The parts are shown corresponding to that zero position of the magnet farthest to the right in Figure 1.

A limit is set, to the extent of movement of the fulcrum edge along the length of the spring tow-ard the lower part of Figure 1, by a set screw |05 which is engaged by the forward ange of the spool.

In assemblage, the spring-supporting block, range adjusting screw, zero adjusting screw, limit set screw and fulcrum block are placed in position before the spring with its magnet and other parts is fastened in place by the cap and the cap bolts. The diaphragm and diaphragm support are assembled and put in place, the housing being closed by the cover. The armature, well and associated parts are preferably put in -place prior to closure of the cover to check the clearance between the magnet and the well.

The standard pressure and the variant, levelcontrolled pressure, or other opposing pressures are then applied.

By testing with maximum and minimum liquid level pressures or other opposing pressures, the range of movement of the indicating needle or recording pen is found and the pen or needle is adjusted on the shaft of the spiral to conform to this range. Adjustment is made by advance or retraction of the fulcrum bar until the range between high and low level indication is satisfactory. The zero point of the needle is then set by the zero-adjusting disc.

With the parts in place and the indicator range and zero point adjusted, the gauge is operated and -any further calibration characteristic of a given installation is eected.

The standard pressure is maintained by well known means. The predominance or the standard pressure on the right of' the diaphragm over the variable pressures upon the left of diaphragm tends to bend the spring to the left in Figure 1 and hence shift the magnet to the left to varying extents depending upon the differential between the variant pressures due to different levels and the standard pressure or due to opposed pressures.

Some of the advantages claimed for the preerred form of my indicator over other indicators of similar purpose, and to greater or less degree true also of the other forms illustrated by me are as follows:

l. The indicator is mechanical in nature. pro- `riding rugged dependable response entirely7 independent of any supplementary actuating forces provided by such mediums as compressed air or electricity.

2. Although basically mechanical in construction, it is practically frictionless in operation, bearing pivots being restricted to two single point contacts within the pressure space and to two jeweled bearings outside of the pressure space.

3. There are no stuillng boxes or other pressure packed movable members projecting through the pressure wall. This eliminates the friction, leakagev and other diiiiculties associated with such types of construction.

4. It is free from gauge glasses, thus eliminating gauge glass troubles and any danger from glass failure or accidental glass breakage.

5. In two of the forms illustrated, it is free from all indicating liquids such as mercury and other water insoluble liquids. Even in the third form it is free from disadvantages ordinarily associated with such liquids, such as accidental loss of liquid by gauge glass breakage or by blowing out oi an indicator tube due to excessive pressure differentials, discoloration of indicating fluid by dirt particles, bleeding of contrasting colors into adjacent liquid medium, etc.

6. Adjustment to conform to the indication of a conventional type gauge or to the actual water level in the steam drum of the boiler can be eiected while the indicator is connected and in operation.

7. One standardized instrument may, by ad- ,iustment, be calibrated to take care of a wide range of liquid levels. This same adjustment may also be used to advantage to compensate for variations in indication due to varying density oi boiler water with boiler pressure or to special conditions of individual boilers.l This adjust ment may also be made While the indicator is in normal operation.

8. Indication is not limited by standard size of gauge glasses or pressure considerations. This permits the use of a clearly visible pointer moving over a liberally proportioned and well illuminated scale. If desired the scale may be colored and illumination may be external or internal. The effect of contrasting color mediums may also be reproduced if desired and, in absence of pressure restrictions, full and direct visibility at all angles may be obtained.

In Figure 1a a spring element is used of a different character from that seen in Figures 145. In this case a sylphon bellows |06 is seated in a recess |01 within the housing cover. The standard pressure is introduced within the sylphon element at 40, and the preponderance oi H2 standard pressure within the sylphon is transmitted through any suitable "sylphon head |08 into engagement with a support for a magnet 48 element is shown as entering recess 2i' in a ring or disc 20' corresponding generally to the diaphragm support 2t of Figure 1, though this element no longer performs the function of supporting a diaphragm.

The pin carries a collar d i corresponding generally to the collar di in Figure 1. This cooperates with a keeper Mill threaded into the ring 2b.

If indicator structurein conjunction with a` calibrated orince or a V notch flow meter be applied to indicate now, the resultant now scale will not be in linear proportion, since the dow is not a straight line function of the pressure difference across the orice nor of the water level above the Weir. The indication may be made directly proportional to the flow for a given flow condition (or some such approximation to it which will lend itself to ready calibration) by compensating at the pressure-sensitive element of the indicator or at the magnetic transmission.

By the rst step above, cooperation could be effected by variable restraint of the magnet movement, as, for example, by introducing a supplemental spring or supplemental springs.

By the second method above probably the simplest way to effect cooperation is by progressive variation of the pitch of the follower or armature to suit the characteristics of a given flow meter as discussed in connection with Figure 10b.

In Figure lb a structure is shown in diagrammatic form also paralleling that of Figure 1, with a spring which may have or may not have provision for adjustment of a fulcrum, and for zero adjustment, but which has one or more supplemental springs H0 attached to the spring at a selected point or points and attached at their opposite ends at Ill to any fixed structure such as the plate 262.

By the construction in Figure 1b the elective component of force from the spring or springs ll may be made to increase and greatly alter the total retarding effect of spring 45' as compared with that of spring 45 against movement of the magnet and free end of the spring to the left. The remainder of the construction in Figure 1b showing transmission between a diaphragm and the spring 45 is or may permissibly be the same as in Figure 1.

'I'he operation of the spring or springs I I0 may supply a considerable part of the retardation eiect or may be supplemental merely to a flat spring of any suitable character.

Whatever the type of spring used, a single spring or a composite of two or more springs may be used such as the flat spring and a plurality of spiraled tension springs such as permissibly used in implementing the diagrammatic showing of Figure 1b. The character of spring i3 actionmaybemadetoreduceanotherwisewide variation in indicator or recording pen movement for the same diiierence in pressure, thus bringing these distances .within the range oi calibration upon a normal scale or record.

In the form of Figures 4 and 5, retardation by springs is wholly eliminated and such retardation as is used is restricted to the progressively increasing pressure ot mercury opposing further change and tending to force the parts back to their initial' position when increasing pressure. upon the surface of a magnet 48' resting in a mercury bath, and upon the surface of the bath within which the magnet rests, depresses this surface, raising the mercury in another part of the bath subject to a pressure. Here either the standard pressure or the variable pressure can be introduced in the magnet compartment by suitable change in the relation of level to armature. The illustration contemplates introducing standard pressure at the right.

In Figures 4 and 5, a casing ||2 is bored at I I3 and I I4 to provide parallel compartments or chambers I I5 and IIS adapted to hold a pool I I1 of mercury. The ends of the bores are closed by threaded plugs IIB and H9.

In order that the mercury from one compartment or chamber may communicate with that in the other, the casing between the bores is transversely bored at |20 and the opening through which this transverse boring is eiIected is closed by a plug |2|.

A variable pressure is admitted to bore H3 through pipe |22 and inlet |23 and a standard pressure or the higher of two variable pressures t be compared is admitted to bore I|4 through pipe |24 and inlet |25.

The magnet 48 noats upon the surface of the mercury in compartment or chamber |I and in the absence of diierence in section or irregularity of weight in parts of the magnet, the magnet will ,float level.

Because the magnet is free to move vertically, its upper and lower planes being parallel in all positions to the initial upper and lower planes of the magnet, and because friction of the magnet poles 56', 51 against the sidesof a well 54 is not a serious matter when the magnet does not cant during its upward and downward movements, the clearance between the poles of the magnet and the walls of the well may be made less in such a construction than in the other iigures and the edges E0', 6I of the pole pieces need not be altered nor trimmed.

With variation of one-and for an orice ilow meter it may be both-of the pressures to which the mercury bath is exposed in the two compartments or chambers, and with equal cross sectional areas in the two bores, the mercury bath in compartment I l5 will rise or fall at the same time and to approximately the same extent as that in the other compartment will fall or rise. Diilerence of the cross sectional areas of the bores may be used to alter the range of indication for the same differences in the pressures in the two bores, reduction of the cross-sectional area of compartment ||5, in which the magnet lies, with respect to that of compartment ||6 increasing the lifting and lowering movement of the magnet and the angular movement of the indicator needle or recorder pen, for example,

` for the same difference in pressure. It follows of course that if the cross sectional area of mercury in compartment ||6 be made selectively variable along the vertical length of the com- 14 partment, the resulting indication will be selectively variable with respect to the difference in pressure between the two compartments and may be made to conform to any variable function of the Pressure such as ow through an oriiice or over a weir.

The reverse is of course also true. This provides for adjustment of the scale range. Zero setting may be eiected through set screws 16, or by withdrawal of plug |2| and insertion of merciu'y or withdrawal of mercury through the opening closed by plug |2I.

The well and armature and their associated parts may be the same well and armature, etc. as seen in Figure 1. Though an indicator needle 12 is shown whose indicator target |26 moves over a scale |21, a recording pen and record may, of course, be used as in Figure 12.

In Figures 6 and 7 the invention is applied to any plain float |28 within a boiler or other cham ber under pressure but with indication or recording outside of the boiler. The oat follows the level |29 of a liquid |30. The iioat arm or rod I3| is rigidly fastened to a magnet 4B2 so that each forms one arm of a crank pivoted at |32. The magnet thus swings angularly to the same extent as the oat arm or bar.

The compartment |33 is formed conveniently by a fitting |34 attached by flanges |35 and bolts |36 to a side of a. casing |31. The compartment communicates with the boiler through a casing opening |38.

The magnet can be of the same character as any shown in Figures 1, 2, 3, 4 and 5 except that for a, considerable angle of swing of the magnet the poles liliI desirably comprise oppositely facing parallel surfaces, in order to avoid danger of the edges striking against the well.

In Figures 6 and 7 the needle 12 is shown as travelling over a transparent scale |38 and is subjected to the light of a lamp |43. The light may pass through any suitable screen such as a colored screen or frosted screen |39' as desired.

In Figure 8 application of my invention to a normal steam drum and water column is shown, by which the water level differences are indicated by differences in pressure on an indicator such for example as that illustrated in Figure l.

The steam drum 4| is connected by pipes |42 and |43, one reliably above and the other below the water level, with a water column |44 from which pipes |45 and |46, again one reliably above and the other below the water level, connect with pressure pots |41 and |48. From these pressure pots pipes |49 and |50 lead to opposite sides o! a diaphragm such as in Figure 1 or a sylphor' bellows as in Figure 1a or to opposite communicating compartments or chambers in a mercury iloat bath such as in Figures 4 and 5, for examples.

In the case of the present illustrations the pipe connection |5llcarrying variant pressure, communicates with the left side of the diaphragm in Figure 1, or outside of the sylphon in Figure la or the left compartment of the mercury bath in Figure 4.

The pipe |49 communicates with the opposite side of the diaphragm in Figure l, or with the inside of the sylphon bellows or with the righthand compartment in Figure 4. As the variant water level communicating with the lower pressure pot |48 drops, the pressure diierence with respect to the constant level in pressure pot |41 increases and the magnet is shifted along the well toward the indicator, i. e., outwardly along the armature, so as to give progressively lower indication for lower variant water level.

In Figure 8 the two pipes |49 and |50 are closed or opened by valves of which but one is shown in the ligure.

No invention is involved in the particular type of indicator or recorder used in any of the forms. Whether the arm 122 of Figure 8 sweep throughout an indicator arc over markings upon the side of a scale. as in Figure 7, or upon the rim of a curved scale as in Figure 9, or carry a pen as in Figure 12 makes little difference.

In Figure 9 the flow pipe |52, |53 is interrupted to provide flanged terminals |54' and |55 bolted about an orice plate |56. The flow pipe ls tapped on opposite sides ofthe plate to pipe the pressure from opposite sides of the orifice to a gauge. It will be recognized that in the form of Figure 8 the `pipe |40 represents a standard maximum pressure pipe, maintained at maximum pressure by condensation and maintaining a constant head reliably above the level of the water in the steam drum. However both of the pressures in the flow pipe form of Figure 9 fluctuate and the intermediate transmission of the indication or the interpretation-for example calibration-of the indicator must take into account the law of variation between the two pressures with different pressure values and different quantities of ow.

In Figure 9 the pipes |51 and |58 carrying the variant pressures on opposite sides of the orifice plate are connected with any gauge of the character described above, intended to operate by reason of opposed pressures with the higher pressure introduced at the right-hand side of the diaphragm, as in Figure l. The indicator scale |59 is cylindrical.

In Figure 10 the invention is applied to recording uid flow or indicating merely the rate of ow of a liquid through a Weir meter, a form of weir being shown at .|60 in weir plate |6| in Figure 10a.

The water in open feed water heater |62 passes through a valve |63 controlled by any storage space float, not shown, through a rocker shaft |64 and rocker arm |65 so as to control the supply of water from the heater entering above the Weir and affecting water level |55. Steam pressure in the heater and meter are equalized by pipe |61.

The illustration in Figure 10 is modeled generally after the illustration in Figure 1 in Yarnall Patent No. 1,143,344, issued June 15, 1915, from which patent other mechanism normally associated with that shown in Figure 10 may be seen and its operation as well as that of the parts shown in Figure 10 may be checked and further explained. Other Yarnall patents to whose structures this invention may be applied are: 1,159,147 to 1,159,150; 1,178,463; 1,200,684 and 1,307,609.

In connection with the types of structure shown in these Yarnall patents, pressure pots |41', |48 of the character shown in Figure 8 are used to carry vapor space pressure as a standard, and variant pressure of the water which is above the weir, through pipes |49' and |50' to one of the gauges.

The differences in water level yield corresponding differences in pressure in pipe |50' but do not give a, true indication of the quantity or rate of fiow, since interpretation of Water level into rate 0r quantity of ow involves application of the 5/2 power or other law of the Weir, according to the shape of the weir selected.

In Figure 10b a ycorrective means is shown for producing a uniform or nearly uniform increase in rotation of the follower or armature due to variation in actual flow, where some such relation (law) as the 5/2 or 3/2 power obtains between liquid rate or quantity of flow and height over the Weir. By this the movement ol the indicator along the scale can be marked in uniform indicator distances of movement per unit of flow or can be nearly enough approximated to such uniform flow movement so as to bring any differences within easy calibration limits.

As previously indicated, the armature may be twisted to different pitches, uniform from end to end so that lmovement of the magnet for the intended distance will yield angular movement t0 an indicator or pen corresponding with the intended gauge extent of the scale.

The armature may also be spiraled irregularly, or according to any progressive rate of change (such as arithmetical or geometrical ratio, or a quadratic relation for example) to give an approximate straight line indication for rates or quantities of flow which do not bear a straight line relation to the variant liquid levels or pressures involved.

The spiraled magnetic follower or armature 55' in Figure 10b progressively reduces in pitch from the bottom of the well outwardly to the spindle or rod 1|, whereby the same increments of movement of the magnet from the bottom of the well toward the top progressively increase in angular eiTect upon the armature according to the law under which the progressive shortening of the pitch has been determined. The follower or armature 55 may thus show variation in pitch according to the law of flow inherent in the character of measure used, or the armature may be twisted to compensate for deviation Which would otherwise take place according to any irregular determination which may be found to give the desired correction in indicator record.

In Figure 11 is shown a very much simpler form of application of a gauge to weir, meter operation than that in Figure 10, with the disadvantage, however, that the gauge is applied at the weir and not at a distance fromthe Weir. The Weir meter is shown in fragmentary form as controlling the position of a magnet along the axis of a spiral armature, operating through a float on the surface of the water above the Weir. This Weir may be any type of weir meter which is under pressure, and maybe any of the Weirs of the Yarnall patents above noted in the settings of these Weirs.

In Figure l1 the meter casing |68 is under pressure and contains a weir chamber |69 leading to a weir |10, a sump compartment |1| into which the water over the weir empties, and whatever other apparatus may be required, varying with the intended use of the weir. This apparatus may include a feed Water heater connected with the weir, sump controlled mechanism by which the flow of liquid from a feed water heater into the weir chamber is regulated and anything else which may be requisite for the intended use.

Upon the surface of the liquid to be metered, at any suitable distance back of the weir such that its presence will not disturb the flow of water over the Weir, I locate a float |12 which is guided-as by wires |13 one on one side of the float and the other on the other side-so as to be free to rise and fall but not to turn. The

17 guides are fastened above the surface |14 orl below the surface or both above and below at |16.

The guides and structure generally are intended to be shown diagrammatically and without the refinements which secure smoothness and accuracy oi' movement.

The float carries magnet 483 by a float rod |18, so that rise and fall of the float lifts the magnet or lowers it along a well 54 containing an armature 55, the conditions being permissibly substantially the same as to the travel of the magnet along the well and armature as in Figures 4 and 5, but with the notable difference that in Figure 11 the magnet is lifted by a separate float.

The magnet may be an electromagnet and is then subject to the disadvantage previously noted. It will be supplied with electric current for its coil 48e through wires 48h, 48a.

The float rod passes through an opening |11 in the top oi the weir meter tank into a compartment |33 on the top of the casing, much as in Figure 6, except that this compartment is shown as located above the Weir casing for straight line movement of a float rod, instead of at the side, for a bell crank float arm operating about a center.

The difference in character of magnet connection and the difference between the swinging bellcrank construction of Figure 6 and the straight line magnet movement in Figure ll is due to the difference of range in water level in the two iigures, the large variation of water level in Figure 6 making it desirable much to reduce the magnet movement, whereas a relatively small variation in level of the liquid above the Weir in Figure 1l permits direct straight line connections between a float on the surface of the liquid in that figure and the magnet.

The magnet 483 carried by the float rod may be prevented from rotary movement by the number of its guides or by the non-circular cooperative cross section oi' the passage through the iloat and a guide, so as to free the magnet poles from frictional engagement with the Walls of the well, or one may use the walls of the magnet poles as guides bearing against the' Well.

In Figure l1 the magnet 483 is lifted or lowered wholly by the oat so that its magnet poles move vertically parallel with the axis of the follower or armature and of the well, so as to turn the follower or armature to a position of minimal reluctance as in the other gures.

With the general construction of Figure l1 an armature or follower should be used oi' the general type shown in Figure 10b, having progressive change of pitch of the armature determined upon the law of relation between the water level height and the quantity of flow in the particular Weir meter which is being used. This will vary with the characteristics, such as the type or angle of the weir opening, and may be typiiied by the /2 power ratio previously referred to.

Where the departure of the needle from. uniform rotation per unit of flow is slight enough to be within the range of calibration, the well may be of the same character as in the other igures. The question of whether or not a spiraled armature of suitable uniform pitch shall be used, such as seen in Figure l, or a spiraled armature of progressively changing pitch, such as that in Figure b becomes a question of policy, in view of the amount of departure of the movement to be indicated from uniform movement per unit of change and the ade than is otherwise available.

quacy of calibration to take care of this difference.

With an orifice ow the law of relation of pressure difference to flow is the square root law. As a result, the progressive change in pitch of the armature will be the reverse of that shown in Figure 10b, though not in the same proportion. The closer pitches will be at the right.

The movement of the magnet transversely along the length of the armature to secure the desired coupling can be eected by hand, whether the well intervenes or not.

Figure 12 is intended for the purpose of showing that an arm suitable for an indicator, such as 12, can carry a recording pen |18 and travel across a moving record disc or moving record strip such as the record surface |18 fed from one mounting roll |80 to another at |8|.

The operation in all of the forms has muchl in common, namely, that the movement of t? magnetic flux transversely to the lines of and lengthwise of the follower or armature di turbs the relation between the follower or ar mature and the magnet, in the previous posis tion of the magnet in which the armature rests in position of minimum reluctance to the flux, and causes the amature to rotate sufciently for the relation of maximum ux to be 're-aestablished.

The extent of rotation required to again establish minimum reluctance depends upon the extent of movement of the magnet causing the flux and upon the pitch of the follower or armature. The mountings of the parts and the ways in which differences in level or in pressure may be made to shift the magnet-and hence the fluxthemselves novel and intended by me to be protected, are illustrative of the wide range of means by which the broader principles of the invention may be carried out.

It will be evident that the extent of variation in range by adjustment of the fulcrum is within the control of the designer, who can vary the effect by the extent of taper of the spring at different points, for example.

It will be evident that all of the structures illustrated are simple, of low first cost and low cost for repairs. Assembly and external adjustment of the zero point and range are easy and when adjustment has been made the conditions are stable. The spring affords combined spring transmission and entire magnet support and makes available more suitable spring material It also eliminates dilculties associated normally with the use of mercury or other auxiliary liquids.

The several Ways of adjusting for zero point and for range are not inconsistent but mair be used together, one type of adjustment for major adjustment and another to secure additional adjustment.

Considerable advantages of the invention as applied to liquid level indication. arise because extremely low level differences can be indicated accurately and the level indication can be given at a distance from the liquid level.

It will be evident that the magnetic align ment of an armature with respect to the ilux oi' the magnet, passing freely through the nonmagnetic walls of the well, affords a simple, cffective and reliable resilient coupling between the magnet and the armature at whatever position the magnet may assume along the length oi' the armature and at the same time frees the 19 armature wholly from pressure conditions, without regard to the extent of pressure within the chamber traversed by the magnet and whether the magnetic flux be shifted parallel to the axis of the follower or armature or only generally along the length of the follower or armature.

Since the difference between the indicator and the recorder does not require more change in structure than the use of a recorder pen upon a travelling record instead of an indicator arrow and since the record to be made is merely a continuous indication, I have aimed to use the word indicator here to cover both forms and to apply whether a visual indication only is given or a record is made. Whatever the form of structure used by which to turn the spiral armature by movement of a magnet along the length of the armature axis, I provide a path of magnetidux across the armature of a width normal to the axis of the spiral and in Width approaching the diameter oi the spiral, in order that the body of the magnetic iiux may not only traverse the metal of the cross section of the spiral presented at the middle of the poles but there mav be magnetic flux outside of this metal of the spiral on both sides of it and toward the respective ends of the spiral, presenting magnetic moments on opposite sides lof the magnetic center line, the one tending to turn the spiral in clockwise direction and the other tending to turn the spiral in counterclockwise direction.

Contrary to the usual cases typical of the structures previously known, where pole pieces of small dimension with respect to the spiral armature cause alignment of a narrow portion of the included spiral essentially along the straight line path of the flux between the poles, the present invention utilizes poles of much greater width and breadth, so as to include the width of the armature and an axial length of the armature approximately equivalent to one-fourth of the spiral pitch within the magnetic field.

'I'he length of spiral influenced by the magnet flux may be greater or less than one-quarter pitch length of spiral but optimum performance will not then be realized.

The larger area and the location of the pole permit not only alignment of the center portion of the armature with the ux as in other devices but also include a spiral section on each side of the center line which is subjected to opposite magnetic torques since the spiral sections at the faces of the magnet will be at an angle of about 45 with the flux line if the one-fourth pitch relation is used.

Practical operation of the indicator requires a strong, compact, independent source of magnetic flux to bridge the gap occasioned by the pressure wall and by the necessary clearances between the magnetic poles and the spiral armature. This calls for a permanent magnet of efiicient magnetic material and a magnetic circuit of minimum reluctance. A horseshoe type magnet satis. iles the latter requirement.

Oppositely disposed bar magnets would not provide a magnetic return path of low reluctance for the ilux and the flux density across the gap fon the same magnetic weight would only be a 'fraction of that provided by the horseshoe type.

Such a structure utilizing the best known magnetic materials would be too inefficient for practical operation of the indicator.

If a low reluctance path be provided for two oppositely disposed bar magnets, the resulting '20 structure would in eilect constitute a composite horseshoe type magnet.

Electromagnets, although theoretically applilcable, are ruled out because of objection to dependence on an outside source of energy. The practical diiilculty of conveying current to and from a movable magnetic coil immersed in a conducting liquid and `contained in a pressure vessel makes this form additionally objectionable.

Sensitivity considerations require that the flux emanatingy from the poles remain as fixed as possible with respect to the poles so as to cause total armature response and minimum tendency for shifting of the ilux concentration on the pole pieces or faces to accommodate slight positional changes. The magnetically soft cores customarily used with electromagnets do not appear to satisfy optimum requirements in this respect.

The completed magnetic circuit is shown in a horseshoe type of permanent magnet which may be referred to as an open ring type permanent magnet or as a permanent magnet having opposite poles directed toward each other. The open ring shown is a ring in which the circuit has been interrupted by removing a portion of the material which would otherwise be required to complete the ring, which has been magnetized and in which under the conditions given the ends ci the otherwise complete ring structure present themselves as oppositely facing poles.

The magnetic screw is in itself old. It is shown, for example, in Norwegian Patent No. 46,537; German Patent No. 515,342 and in U. S. Patent No. 2,154,678.

The distinctions and the reasons for the distinctions of the present invention from such structures will be clear from the following discussion.

Armature response in the patents above in general results from the continuous alignment of a narrow cross sectional band of spiral armature with longitudinal movement of a transversely directed iield of magnetic flux. Maximum sensitivity of operation for this condition requires minimum clearance between magnetic armature and poles or pole pieces conforming to the adjacent section of the spiral precisely as indicated in the illustrations. If the gap between the armature and magnetic poles'be increased, the reluctance of the magnetic circuit is increased, the ux is decreased, and a loss of torque and sensitivity results. Interposition of a pressure wall and necessary clearances between poles and armature as applied to the present case would necessarily increase the gap and consequently would result in the lowering of the level of performance of the structures of these patents.

In the present case a comparatively long section oi the spiral armature (approximately onefourth pitch) is contained within the gap between broad poles oi' a strong Alnico magnet (the most efficient commercial permanent magnet material available to date). The fiux is not guided or directed to the opposite edges of the included armature as in the patents, but streams across the gap and acts upon the entire included spiral of approximately one-fourth pitch length. The spiral section at the magnetic Acenterline of the poles is aligned directly across the poles and in this respect behaves similarly to the patent structures. A 45 twist of the spiral on each side of the center line is also in the magnetic iield and the spiral armature is thereby subjected to equal and opposite turning moments. The relation of magnetic pole width to spiral pitch is selected by l6-16a, a previously existing form of magnet l0 poles operating upon a twisted spiral between them is shown. As is usual in such cases, the magnet poles are both short in extent along the axis and thin, i. e. they not only do not extend far along the armature axis but they do not exl5 tend iar about the amature. The pole areas are thus not only circumferentially small and small in their axial extent but are small in their total areas. They concentrate the'iiux upon that intermediate portion of the spiral armature which is immediately adjacent at the middle of the poles. As a result they give substantially a straight line ilux path from one pole to the other through the included section oi the armature.

For comparative purposes, unit eiective magnetic pole area is assumed and the magnetic force ls assumed to be unity at minimum gap distance. In the equilibrium position of the armature, the moment arm of the magnetic force is zero, the

spiral section being in alignment with the iiux.

The torque is of course also zero.

In Figures 13 and 13a it will be seen that the poles |82, |83 have a total width substantially equal to the thickness of the strip |84 from which the armature is spiraled. The gap indicated has been made excessive so as to accommodate an intervening pressure Well, as would have to be the case if this form is to be compared with that of the present invention. The length of the pole pieces parallel to the armature axis from points |85 to points |86 is trivial as compared with the pitch of the spiraled armature. The volume of the flux or the cross section of the flux, as it may be considered, is very small as compared with the section of the spiraled armature through is which the flux distributes.

The structure of Figures 13 and 13a is best suited to conditions where the poles can be broughtcloselup to the intervening spiraled armature and where the entire ux can be concentrated for this reason upon a short section of armature. As will later be pointed out, it is not well suited to a construction where the armature is surrounded by a protective well which makes it necessary to space poles from the spi- 5,5

raled armature to such an extent that the magnetic iiux cannot be concentrated upon the armature. In such a case as that in Figures 17 and 17a, the structure of Figures 13 and 13a would be inadequate for the purpose.

In Figure 14 the magnetic force for equilibrium corresponding to Figures 13 and 13a is shown. The magnetic force is given per unit effective pole area. The magnetic force exerted is represented by the figure at |81 in the maximum position when the armature is aligned with the flux. The curve in Figure 14a indicates the eiective force exerted by the pole pieces upon the armature with movement of the poles along the axis of the armature a distance equal to one- The moment arm of the iiux tending to turn the spiraled arma-` ture about its axis ls zero when the transverse section of the armature is in alignment with the flux. As the magnet is moved along the spiraled armature the moment arm increases, reaching a maximum at some such point as |89 at a distance corresponding to somewhat over one-eighth of the spiral pitch distance. The torque exerted upon the spiral armature tending to turn about its axis under the conditions in the figures above ls represented in Figures 16 and 16a. This is a product of the magnetic forces and the moment arm. The position of Figure 16 is equilibrium position, in which the torque is zero and there is no tendency to turn the spiral armature.

As the magnet is moved along the axial length of the spiral arm, the torque increases rapidly, reaching its. maximum at some such point as |90, at somewhat over one-thirty-second of the spiral pitch, and gradually decreasing to a minimum again at, let us say, |9 I, approximately onefourth of the spiral pitch. Y

Sensitivity of response of the armature to longitudinal magnet movement is a function of the restoring torque with relative displacement from the equilibrium position. In the case of Figure 14, the magnetic force decreases from assumed unity per unit of area with relative displacement of magnet and armature and the moment arm increases from zero with this progressive displacement, as shown in Figure 15. The resulting form of the torque curve with respect to change of relative position of magnet and armature is as shown on Figure 16. It will be noted that the maximum restoring moment is developed for a magnet movement of slightly 'over one-thirty-second of the spiral pitch distance.

In Figures 17 to 21, 17a and 18a inclusive, the schematic views shown apply to the present form of the invention as distinguished from the prior art type discussed in connection with Figures 13, 1311; 14, 14a; 15, 15a and 16, and 16a.

In the present invention the thickness of the pole pieces from |92 to |93 preferably is several times the thickness from |96 to |95 of the strip material from which the spiral armature od magnetizable material is constructed, (as this exists in the prior art of Figure 13, for example) and my best results have been obtained when the chord distance approaches the diameter of the armature. This gives a much wider band of ilux across throughout the depth or height of the magnet pole pieces |82' and |83.

The extent of the pole pieces from` |85' to |86' parallel to the axis of the armature is also many times the extent in the prior art form from |85 to |86 (see Figure 13a) and my best results have been attained when the pole pieces approximate ogre-fourth of the pitch of the spiral armature 4'.

Between the spiral armature and the pole pieces there is space at |96 for the stationary pressure shield, within which space the armature rotates and outside oi which the pole pieces move parallel to the axis of the armature. These general relations are shown in Figures 17 and 17a.

The illustrations in Figures 17, 17a; 18, 18a; 19; 20 and 21, which schematically show the present invention, form a basis for contrast with the prior art form of the immediately preceding schematic iigures. Of these iigures, Figures 17 and 17a show the contrast between the Wider pole pieces, extending farther along the armature axis, of the present invention and the pole pieces auoacea of small dimension in both directions and 'of small cross section in Figures 13 and 13a.

Figures 17, 17a yield a wide range of variant magnetic i'orces and movements effective on the spiral section included in the magnetic iield of large cross section provided by the present invention.

Assuming, as before, that unit eiective magnetic force per unit area obtains for minimum gap distance, we find this unit force acting on the edge of the spiral to be maximum at the magnetic centerline and reducing toward the magnet sides because of increasing gap and decreasing projected armature areas between the spiral edge and the centerline, the spiral edges acting farther and farther away from the pole faces as the distance along the axis increases on opposite sides of the centerline.

Figures 18 and 18a show the relative magnitude of these magnetic forces and the approximate totals at the various spiral sections within the magnetic gap. The moment arm of these respective total forces is zero at itil at the centerline of the magnet (Figure 19) and increases in opposite directions on each side of the centerline as there shown.

The moment arm reaches a maximum at the limits i90 and its at each side of the magnet as shown. in Figure 19. The resulting torque, which is the product of the total forces and corresponding moment arms at the respective sections, increases in opposite directions at each side of the magnetic centerline and reaches a maximum at the pole limits, as indicated at 2d@ and 20E in Figure 20. The spiral assumes a balanced position of equalization of opposed moments which corresponds to the position of lowest reluctance of the magnetic circuit.

In the entire operation described, it makes no difference which be the leading and which the trailing edge of the pole pieces nor, correspondingly, does it matter whether the magnet is moving upwardly or downwardly, the character of operation of the armature by the magnetic forces set up being the same.

In the case of Figures 17 and 1711, axial magnetic movement of the magnetic poles with respect to the spiral armature adds to the existing torque on one side of the magnetic centerline and subtracts from the existing torque on the other side, at or near the maximum obtainable rate.

Although the torque per unit magnetic force per unit area may be comparable for the prior art discussed in connection with Figures 13 to 16 or even less in the present invention, the larger eiective pole and armature areas of the present invention provide for much larger total magnetic restoring moments. It will be noted that the initial rate of increase in the restoring torque with relative displacement of the armature and the magnet is high and likewise contributes to sensitivity of response.

The curves of Figure 20 illustrate the development of this greater restoring torque. The left hand curve 202 shows the relative torque values developed in the spiral armature within the magnetic gap. It will be noted that the torque is zero vat the magnetic centerline 203 and ncreases equally in opposite directions to a maximum at 200 and 20|. It will thus be evident a distinct advantage exists in having the axial extent of the magnet pole piece the greater part of a quarter of the pitch distance.

The restoring torque comparable to that in Figures 13 to 16 may be obtained by totalling the unbalancing moments per unit edge area of spiral with respect to magnetic movement. This can be done graphically by dividing the spiral length in the magnetic gap into increments 204 of length corresponding to the assumed unit length of the magnet represented in Figures 13 and 13e and adding the mean torque values of these increments as they become unbalanced moments with respect to magnet movement.

To illustrate the above, take the case of magnet movement corresponding to one unit l of length in Figure 20, which, for the relations shown, corresponds to one-thirty-second or the distance of the spiral pitch. A positive torque loss of t1 results from this movement, accompanied by a simultaneous gain in negative torque t2 of approximately the same magnitude. The net relative restoring torque for this magnet movement would be tr-l-ta. This point is plotted on the torque vs. magnet-movement curve for the movement of one-thirty-second oi the spiral pitch distance (as shown by Figure 21). Further magnet movement develops additional restoring torque as indicated by the completed curve of the same gure.

It will be noted that the maximum restoring moment occurs at a magnet movement equal to one-eighth of the spiral pitch from the equilibrium position. This is advantageous in that it provides latitude of positive armature control and response for rapidly changing magnet positions as compared with the comparable cases in Figure 16.

The utilization of the magnet poles of relatively large size with respect to spiral armature dimensions of the present case contributes important advantages aside from the foregoing distinctions. It permits retention of higher unit magnetic forces and provides greater assurance of permanency of magnetic properties over the life of the instrument. These advantages further amplify the improved performance over that of the patent structures and in themselves provide the practical elements which stimulate commercial acceptance of a device. The form of the magnet used furthermore conforms to simple design and elcient proportioning of magnet material. This in turn implies low cost of manufacture commensurate with high level of performance.

A more detailed mathematical analysis of forces and moments can be preparedk if it be desirable to distinguish the present invention from the structures shown and described in the Norwegian and German patents and in the patent to Hawthorne and Campbell previously referred to. However, the effectiveness of such an analysis must depend upon recognition of the basic diierences indicated herein.

It would seem to be clear that the differences between the operation of the structure of these prior patents and the operation of the present invention is .a radical difference necessary for operation where there is to be a large gap to provide for a pressure protective well and is a difference in kind and not a mere difference in degree. The structures of the type shown in the Norwegian and German patents or in Hawthorne above would be inoperative for my purpose and could not be made operative without the radical change in character of the ilux ileld represented by the present invention.

One noticeable difference between the structure and method of Figure 13 and that of Figure 

